Advertisement

Advertisement

Folic acid may raise chance of twins

Pregnant women who take the recommended folic acid supplements may be more likely to have twins, say researchers in Sweden.

The supplements cut the risk of birth defects, but twins have their own problems – they are more likely to be premature, have low birth weights and suffer from cerebral palsy.

Photo&colon; Stone

Many women take the vitamin folic acid before and during pregnancy to reduce the risk that their babies will have neural-tube defects, such as spina bifida. In the US, the compulsory addition of folic acid to breakfast cereals and wholemeal bread since 1998 has reduced the incidence of spina bifida by 19 per cent. This has increased pressure on other nations to follow suit.

But the costs could outweigh the benefits, especially in countries where spina bifida is relatively uncommon, according to Bengt Källén of the Tornblad Institute in Lund. He and his team have looked at records from the Swedish Medical Birth Registry, which has gathered data on the use of medicines by pregnant women since 1994.

Advertisement

According to the records, 2569 women said they used folic acid supplements. The rate of twin births for these women was 2.8 per cent. In the general Swedish population, however, 1.5 per cent of births in the late 1990s were twins.

Multiple ovulation

The reasons for the difference are not clear. Källén’s team tried to allow for other factors – older mothers and those using IVF, for instance, who are already more likely to have twins. It is possible that folic acid somehow increases the probability of multiple ovulation or implantation of more than one egg.

If folic acid does increase the number of twins, the supplements could cause more problems than they solve. Källén calculates that if 30 per cent of 100,000 women in Sweden took folic acid supplements, there would be 225 extra pairs of twins. These 450 babies would often be premature, have low birth weight and an increased risk of cerebral palsy. At most, only four or five spina bifida cases would be avoided.

Källén says more research is needed to pin down the effects of folic acid tablets. “I think one should consider the pros and cons – especially in areas like Sweden with a low rate of spina bifida,” he says.

However, Nicholas Wald, an expert on preventive medicine at St Bartholomew’s Hospital in London, is not convinced by the Swedish research. He would like to see a much larger study looking only at younger women who all have a similar expected rate of twins and are unlikely to have had fertility treatment.